Project Summary & Abstract Pregnant and postpartum women living with HIV (WLWH) and latent tuberculosis (TB) infection (LTBI) are at high risk of progressing to active TB. Safe and effective treatment during the latent phase is critical to preventing active TB, in addition to reducing TB-related maternal and infant morbidity and mortality. Isoniazid (INH) has been used for decades to treat active and latent TB infection, and there are several international efforts to expand the use of INH preventive therapy (IPT) to address global TB burden. A recent large-scale clinical trial in pregnant and postpartum WLWH revealed high rates of severe hepatotoxicity with IPT (~6-7% vs. <1% based on historical data in non-pregnant adults) during the postpartum period (IMPAACT P1078). Available evidence suggests reactive INH metabolites are involved in the development of hepatotoxicity with INH. However, there are currently no data on the pharmacokinetics of INH metabolites in pregnant or postpartum women. Additionally, there are immunologic and metabolic changes that occur during and after pregnancy, which may further predispose this population to a higher risk of developing hepatotoxicity during the postpartum period. Mechanistic insights are needed to inform the safe use of IPT in this population. This proposal will leverage existing samples collected under the P1078 study to comprehensively examine PK, immunologic, and metabolic changes in pregnant and postpartum WLWH on IPT using a case-control design. The following aims are proposed: (1) to quantify INH metabolite PK in pregnant and postpartum WLWH receiving IPT, (2) to identify biomarkers of hepatotoxicity in pregnant and postpartum WLWH receiving IPT, and (3) to model relationships between INH metabolite exposures, toxicity biomarkers, and the development of hepatotoxicity. In Aim 1, INH metabolites will be measured from intensive and sparse PK samples to quantify INH metabolite PK in pregnant and postpartum women. In Aim 2, an enriched case-control design will be applied to evaluate baseline and on-treatment biomarkers of hepatotoxicity using metabolomics and cytokine arrays. Aim 3 will integrate data generated from Aims 1 and 2 to examine relationships between INH metabolite exposures, metabolic and immunology biomarkers, and the development of hepatotoxicity. This work will be complemented by a mentoring team comprised of experts in pharmacology, metabolomics, immunology, and statistics, in addition to collaborators from the P1078 study. Dr. Brooks will also pursue focused training and coursework in biostatistics, PK modeling, metabolomics, and hands-on experience in the laboratory setting. Dr. Brooks's career goal is to become an expert in the clinical pharmacology of TB medications and mechanisms of immune-mediated adverse drug reactions. The proposed work in Dr. Brooks's K08 application will provide her with a strong foundation to develop into an independent investigator in this field. Furthermore, this work will address critical knowledge gaps in a vulnerable population to help support the safe uptake and expansion of TB preventive therapies on a global scale.